Image guided medical and surgical procedures utilize patient images obtained prior to or during a medical procedure to guide a physician performing the procedure. Recent advances in imaging technology, especially in imaging technologies that produce highly-detailed, two, three, and four dimensional images, such as computed tomography (CT), magnetic resonance imaging (MRI), fluoroscopic imaging (such as with a C-arm device), positron emission tomography (PET), and ultrasound imaging (US) has increased the interest in image guided medical procedures.
Typical image guided navigation systems generally require a dynamic reference frame to track the position of the patient should patient movement occur during the assisted procedure. The dynamic reference frame is generally affixed to the patient in a generally permanent or immovable fashion. The dynamic reference frame may also be used as a fiducial marker and may, therefore, be attached to the patient during the acquisition of pre-operative images. This enables the image space to be aligned with patient space during the navigated procedure.
Various instruments may be used during an operative procedure that are desired to be tracked. Image data is generally acquired, either intra-operatively or pre-operatively, and the instrument is generally illustrated, and superimposed on the captured image data to identify the position of the instrument relative to the patient space. Therefore, the instrument may include tracking sensors, such as electromagnetic coils or optical detection points, such as LEDs or reflectors, that may be detected by a suitable tracking system.
Other types of navigation systems operate as an image-less system, where an image of the body is not captured by an imaging device prior to the medical procedure, such as the device disclosed in U.S. patent application Ser. No. 10/687,539, entitled Method And Apparatus For Surgical Navigation Of A Multiple Piece Construct For Implantation, filed Oct. 16, 2003, incorporated herein by reference. With this type of procedure, the system may use a probe to contact certain landmarks in the body, such as landmarks on bone, where the system generates either a two-dimensional or three-dimensional model of the area of interest based upon these contacts. This way, when the surgical instrument or other object is tracked relative to this area, they can be superimposed on this model.
Most types of orthopedic medical procedures are performed using conventional surgical techniques, such as spine, hip, knee, shoulder, a synovial joint, and a facet joint. These techniques generally involve opening the patient in a manner to provide adequate viewing by the surgeon during the medical procedure. Use of the navigated procedure may enable more precise and accurate placement of an implant within the patient and may also enable surgery with diminished visualization.
Image guided procedures generally require the use of instruments and other portions that are tracked with the aid of tracking sensors. The tracking sensors, however, are generally affixed to the instrument. Thus the position of an attachment to the instrument, such as an implant or reamer, is known only through knowing the position of the instrument. Thus the tracking system must be calibrated for each of the attachments. If the instrument is straight, cylindrical, and the attachment is concentric, this can be done by touching the end point on the attachment with a tracked probe and then rotating the instrument about its axis in a tracked calibration block to determine the axis of the cylindrical shaft. Often, however, the instruments are not straight and it is desirable to still calibrate the attachment in the tracking system.